(e, 3e) test on e-e correlations in helium

The angular variations of the five-fold differential cross section obtained by using different wave functions of helium are compared with experimental data. It is found that in the coplanar geometry two kinematical arrangements, (i) equal energy sharing between the two ejected electrons with one of them ejected along the momentum transfer direction and the other along varying direction and (ii) the Bethe ridge condition with fixed sum of ejected electron energies and varying angle between them, are very sensitive to e-e correlations contained in the target wave function. This comparison has been used to show that open-shell class of wave functions better incorporate e-e correlations than the closed-shell class.     

A polymer thin-film technique to study the micromorphology of core/shell latexes

A series of poly(styrene)/poly(styrene-co-acrylonitrile) core-shell latexes were synthesized by seeded emulsion polymerization. The dried latex was dissolved in toluene and then cast on the surface of water to form a very thin film (60–90 nm). Phase separation in the thin film was studied by transmission electron microscopy (TEM). Electron micrographs of these thin films yielded fine structure and interesting morphology that was unattainable by ultramicrotoming of the corresponding compression-molded specimens. Glass transition temperatures and percent grafted polystyrene were correlated with the TEM results. As grafting increases, mixing of the two phases improves, with the resulting T_g value being between the two T_g's of poly(styrene) and poly(styrene-co-acrylonitrile).     

Functional polymers and sequential copolymers by phase transfer catalysis. XXVI. Synthesis and characterization of thermotropic liquid crystalline polypodants

Thermotropic liquid crystalline (LC) polyethers and copolyethers have been synthesized from 4,4′-dihydroxy-α-methylstilbene (HMS) and α,ω-dichlorooligo(oxyethylene)s having between 2 and 5 as well as 8.7 oxyethylene units. Copolyethers were prepared from a 1:1 mol/mol ratio of two dissimilar spacers. These polymers have been prepared by a phase transfer catalyzed (PTC) polyetherification of bisphenols with these electrophiles by utilizing 50 mol% tetrabutylammonium hydrogen sulfate per phenol group. Kinetic experiments with either 5 or 50 mol% catalyst vs phenol groups in the polyetherification of 4,4%-isopropylidenediphenol with 2-chloroethyl ether have shown that a change in catalyst primarily affects the rate of reaction, with 50 mol % being faster. The prepared polyethers and copolyethers are soluble in common organic solvents. Both polyethers and copolyethers are crystalline. Polymers prepared to contain tetraoxyethylene spacers exhibit monotropic LC behavior. Copolymers prepared to contain tri- and tetraoxyethylene spacers (1 : 1 mol/mol) [PE34] were the only polymers exhibiting enantiotropic LC behavior. Longer spacers tend to destabilize the phase transitions, as suggested by the dependence of thermal transition temperatures upon the differential scanning calorimeter rate. All prepared polymers act as podants in solution, measured by picrate extraction experiments. Solid state complexes have been prepared from the polymer with a pentaoxyethylene spacer [PE5] and PE34 with LiCF₃SO₃. PE5 can dissolve LiCF₃SO₃ in the range of 0.21–2.2 mol salt/mol polymer (m.r.u.) [S/P] without the observation of free salt. PE5 complexes of/or below S/P of 0.43, upon annealing at room temperature, exhibited the two melting transitons observed in the polymer alone. PE5 complexes of/or above S/P of 0.77 only exhibited a T_g. The T_g of PE5 complexes were found to change nonlinearly with S/P, while T_m1 changed linearly. T_m2 was independent of S/P. Only one complex with PE34 gave two transitions (T_m2,Tⁱ) in dynamic DSC experiments. Other PE34 complexes followed a behavior similar to PE5 complexes.     

Electron-impact fragmentation of the bicyclo[4.1.0]heptane-2-one system: Correlations with photochemistry

The low resolution and complete high resolution mass spectra of a series of methyl and deuterium substituted bicyclo[4.1.0]heptane-2-one derivatives have been measured. An attempt has been made to test the operation of a fragmentation process analogous to the known photochemical rearrangement, and to determine if the substitution effects critical to the photorearrangement also influence the electron-impact process. The fragmentation pattern of these conjugated cyclopropyl ketones is detailed and the influence of the cyclopropyl ring is discussed. It is suggested that electron-impact-induced rearrangements which are analogous to photochemical transformations will be relatively low energy processes and will remain prominent at low ionizing voltages.     

Synthesis of high purity single-walled carbon nanotubes in high yield

A simple method for the synthesis of high purity single wall carbon nanotubes has been developed by using nickel formate as a precursor for the formation of nearly mono-dispersed nickel seed-nanoparticles as catalysts in the CVD growth process.     

Hydrogen bonding in transient bifunctional hypervalent radicals by neutralization-reionization mass spectrometry

Neutralization—reionization mass spectrometry is used to generate hypervalent 9-N-4 (ammonium) and 9-O-3 (oxonium) radicals derived from protonated α,ω-bis-(dimethylamino)alkanes and α,ω-dimethoxyalkanes, which exist as cyclic hydrogen-bonded structures in the gas phase. Collisional neutralization with dimethyl disulfide, trimethylamine, and xenon of the hydrogen-bonded onium cations followed by reionization with oxygen results in complete dissociation. Bond cleavages at the hypervalent nitrogen atoms are found to follow the order CH₂-N>CH₃-N>N-H, which differs from that in the monofunctional hydrogen-n-heptyldimethylammonium radical, which gives CH₂-N>N-H>CH₃-N. No overall stabilization through hydrogen bonding of the bifunctional hypervalent ammonium and oxonium radicals is observed. Subtle effects of ring size are found that tend to stabilize large ring structures and are attributed to intramolecular hydrogen bonding.     

Controlled functionalization of gold nanoparticles through a solid phase synthesis approach

A novel solid phase synthetic strategy was developed in this work for controlled functionalization of gold nanoparticles.     

Die Bestimmung der Oxybutters?ure

Ohne Zusammenfassung